Theory of thermal remagnetization of permanent magnets

A self-consistent mean-field theory explaining the thermal remagnetization (TR) of polycrystalline permanent magnets is given. The influence of the en vironment of a grain is treated by an inclusion approximation, relating the held inside the grain to the local field outside by means of an internal d emagnetization factor n. For the switching fields and the fluctuations of t he local fields around the mean field, Gaussian distributions of widths sig ma (s), and sigma (f), respectively, are assumed. The isothermal hysteresis curve, the recoil curves, and the TR dependent on the model parameters n, sigma (s), and af are calculated. Furthermore, the influence of the initial temperature and the strong dependence of the TR on the demagnetization fac tor of the sample are studied, and it is shown that for reasonable paramete r sets TR effects up to 100% are possible. The theoretical results correspo nd well with the experimental situation. (C) 2001 Elsevier Science B.V. All rights reserved.